The invention relates to a supporting element to be used in building constructions, comprising a metal inner tube telescoping in a metal outer tube.
An element of this type is generally known and is used for various purposes in concrete construction works, for example, for vertically supporting forms for casting concrete floors, for erecting scaffoldings, or for providing support in a horizontal plane between, for example, two vertical walls.
The known constructions made of aluminium are formed by a set of telescopingly extending metal tubes having clearance, whose ends may comprise a fixed or hingeable foot or head plate and which tubes may further include means for not permitting the tubes to depart from each other. So-called adjustable and shoring struts and also standards for so-called frames in scaffoldings, as well as telescopic tube constructions for supporting vertical walls are generally known examples of said supporting elements.
In the known constructions for temporary support, preferably free adjustable struts, that is to say, without the need for much time-consuming header and shoring ties, are utilized to save time during forming and dismantling. The load-bearing capacity of a thus loaded adjustable strut is thus determined by the failure load as a result of the buckling of the adjustable strut, and which failure load is especially determined by the ratio of buckling length to the moment of inertia of the tubes. Because adjustable struts are normally to be installed and removed manually, in the known construction it is pursued to manufacture a lightest possible adjustable strut which possesses maximum loadability. For the known supporting elements a round tube is selected for this purpose, which tube has a maximum diameter and a small wall thickness, so that a tube construction is obtained having a maximum moment of inertia in all directions.
However, a relatively small wall thickness has appeared not to be capable of withstanding rough handling on the building site. Dents thus developed impede the telescopic operation of the inner tube relative to the outer tube. These deformations of the outer tube are usually caused by struts falling over or falling on top of each other when placed in the appropriate transport containers. Especially the protruding foot and head plates cause locally sharp dents during this operation. As a result, the telescopic operation of the tubes is rendered more difficult, if not completely impossible. In order to obtain a favourable load-bearing capacity of the construction, it is important that there be minimum clearance between the outer and inner tubes, but minor deformations of the outer tube may already terminate the telescopic operation of the tubes. Furthermore, generally as a safety precaution, the end of the inner tube sliding in the outer tube has a protuberance that is incapable of passing through the hole at the top of the outer tube, so that the inner tube is withheld from completely sliding out of the outer tube. A relatively large tube diameter further has the disadvantage that such constructions are hard to handle by hand.